View source for Puzzle 2005 8 285 - Answer

{{NHJ|
|mainauthor= '''A.A.M. Wilde, R.B.A. van den Brink'''
|edition= 2005:8,285
}}
[[Image:Puzzle_2005_8_285_fig1.jpg|Figure 1|thumb]]
[[Image:Puzzle_2005_8_285_fig2.jpg|Figure 2|thumb]]
An otherwise healthy 24-year-old man was referred
to our hospital because of drug refractory spells
of palpitations accompanied by dizziness. These
symptoms recurred several times a month and were
terminated with intravenous adenosine. Figures 1 and
2 show the ECGs during palpitations and during
normal conditions, respectively.

'''What is the most likely diagnosis and how can it be treated?'''

==Answer==
[[Image:Puzzle_2005_8_285_fig3.jpg|Figure 3|thumb]]
The above information should raise the suspicion of a
Mahaim fibre. This is an accessory pathway with AVnode-
like properties. Due to its decremental properties
preexcitation is subtle and may even be absent. The
Mahaim fibre only conducts in an antegrade fashion
and usually has a long course, extending from the free
wall of the right atrium across the tricuspid annulus to
the right bundle. Consequently, tachycardias run in
an antidromic direction and generally show an LBBB
morphology with a superior axis. Although the original
publications by Mahaim, who was a contemporary of
Wenckebach, were on nodoventricular and fasciculoventricular
fibres, his name survived all new insights
and nomenclature published thereafter and is still used
to paraphrase an entire family of accessory pathways
with AV-node-like behaviour.
In this patient the combination of subtle signs of
preexcitation in the resting ECG, absent Q wave in
leads I, V5 and V6, an RS in III and the wide QRS
tachycardia with LBBB morphology and left-axis
deviation is highly suggestive of the diagnosis of
Mahaim fibre. During invasive electrophysiological
testing a Mahaim fibre was identified running from the
anterior site of the tricuspid valve annulus to the distal
right bundle. The Mahaim bundle was successfully
ablated at the level of the annulus. The ECG shown in
figure 3 no longer reveals the subtle signs of abnormal
initial activation or preexcitation. During follow-up,
the patient remained free from symptoms.